1. Field of the Invention
This invention relates to a roll control device having particular application to aircraft possessing a cropped, arrow-type planform with thin leading and side edges, control being achieved by altering the wing surface area which a shed vortex system provides lift against.
The problem of roll control is evident with all aircraft, with solutions being varied and numerous. Generally, tip- and trailing- edge ailerons, partial span flaps, horizontal tails or spoilers are used to provide rolling moments for maneuverability and control in aircraft having transonic and supersonic capability. There are, however, disadvantages to these solutions. Specifically rolling moment effectiveness falls off as the angle of attack is increased. The devices are also susceptible to reversal where deflection of the control surface induces elastic distortions so as to create an aerodynamic moment of the opposite sense to the control surface deflection and of such magnitude that no resultant control moment is produced. Furthermore, the devices produce an unfavorable yawing moment when deployed. The tip aileron poses a separate problem since it is an added-on aerodynamic surface which, under the expected local flow conditions, would produce increases in the local loadings. Hence, a structural problem could result.
It is therefore an object of the present invention to disclose a roll control device having increased rolling-moment effectiveness at the higher angles of attack.
A further object of the invention is to provide a device producing increased roll-rates over a wide angle of attack range.
An additional object of the invention is to provide a roll control device not as susceptible to reversal as prior devices.
Another object of the invention is to provide a roll control device which produces no or favorable yawing moments in flight.
A further additional object of the invention is to provide a device which utilizes leading- and side-edge shed vortex systems to impart rolling moments to an aircraft for maneuverability and control.
2. SUMMARY OF THE INVENTION
Vortex flows, such as those associated with edge separation, and their accompanying flow re-attachment, are encountered at many points within the flight and maneuver envelopes of high-speed aircraft. While performing wind tunnel tests to determine if a mathematical analogy correlated with empirical data, it was discovered that vortex flow around the side edges of an aircraft having a cropped arrow planform produced lift. Hence, it was hypothesized that if there was a method of weakening the vortex flow on one wing panel, a significant amount of rolling moment could be produced, especially at the higher angles of attack where ailerons are generally ineffective. It was discovered that alteration of the crop angle, that is, a change in position of the wing tip side edge from parallel with the longitudinal plane of symmetry of the aircraft to another position, of one or both wing panels to create an asymmetrical aircraft planform produced such a rolling moment. In the present invention a powered aircraft having a conventional fuselage, is provided with a segmented wing projecting from each side of the fuselage. Each wing includes a main wing panel having a swept leading edge and an outboard tip control panel pivotally connected to the main wing panel near the outboard edge thereof for rotation in the wing areal plane. The tip control panel possesses a substantially straight tip edge which, when positioned parallel with the longitudinal plane of symmetry of the aircraft, is subject to the vortex flow present there and hence contributes to wing lift.
By varying the position of a tip edge so that it no longer parallels the longitudinal plane of symmetry but rather extends rearwardly and inwardly, the wing surface area behind the leading edge tip subject to vortex flow is reduced resulting in a similar reduction in wing lift. By positioning the other tip control panel in asymmetrical relation to the first, a rolling moment will be imparted to the aircraft in the direction of the wing possessing the smaller lift component.
Since vortex lift increases with angle of attack, rolling moment effectiveness does not fall off as the angle of attack is increased. Furthermore, yawing moment is absent or favorable. Additionally, the devise is not as susceptible to reversal since roll control is accomplished without deflection of a surface into the air stream.